1. Field
The present invention relates generally to connecting peripherals to host computers, and more specifically to connecting a multiple-channel connector of a host or expander to a plurality of peripheral devices.
2. Related Art
Serial Attached SCSI (SAS) is a storage interface for transferring data between a host computer and peripheral devices such as hard drives, optical drives, tape drives, scanners, and the like. The devices are ordinarily connected to the computer by a cable, where one end of the cable plugs into a SAS port connector on the computer, or into an interface module that communicates with the computer. The other end of the cable plugs into an SAS port connector on the peripheral device. Each SAS port connector may include multiple channels, and each channel may include one or more conducting strips or pins. The cable connects the strips or pins of an interface connector or port on the computer or interface module to the corresponding sockets or pins of an interface connector or port on the peripheral device. The pins may be metallic protrusions, metallic surfaces on a printed circuit board, or the like. Sockets accept the pins when the cable is connected to the connector or port. The SAS protocol uses SCSI (Small Computer System Interface) commands transmitted via high-speed serial communication.
The host computer is referred to as an “initiator” because it initiates commands and data transfer operations. The peripheral device is referred to as a target, and receives the commands. The target includes at least one port that in turn includes connection points, and also includes one or more storage devices, e.g., hard disks or tape drives, on which the data is stored. The target device writes the data received from the initiator on the storage device(s), and reads data requested by the initiator from the storage device(s).
Interconnection of devices with host systems, and interconnection of SAS devices, are known in the art. Host-bus adapters, e.g., interface cards for use in a personal computer, may have an SAS interface port. A host-bus adapter may have, for example, one connector that includes channels or “lanes” for multiple devices to communicate with the host in parallel. There may be, for example, four channels in each connector. Connectors may have fewer channels, e.g., two channels, or more channels, e.g., eight or sixteen channels per connector. The connector may interface with the device via a cable, where the cable connects each of the channels to a corresponding portion of a port connector on the device. Existing SCSI parallel technology may use direct attachment via a cable or daisy-chaining via a sequence of cables to connect multiple tape drives to a host computer. However, direct-attachment is relatively expensive and daisy-chaining involves risks such as of shutting down the entire chain if the first peripheral device needs replacement.
Existing SAS expanders may perform packet switching to route data from the host to the peripheral devices. The peripheral devices may be SAS initiators or targets. SAS expanders may locate an end device directly, using a physical connection e.g., via a cable, or using a routing table to direct packets of data to the end device. SAS expanders are, however, relatively bulky, expensive, and use rack space and AC power. Furthermore, existing SAS cables and expanders connect multi-channel host-bus interface connectors to multi-channel peripheral connectors. However, some peripherals have single-channel connectors that are incompatible with the multi-channel device connectors of existing SAS cables and expanders.